Semiconductor device and method of manufacturing same

ABSTRACT

A semiconductor device includes: a first conductive type semiconductor device; a first conductive type drift region formed by epitaxial growth on the semiconductor substrate; a plurality of first conductive type vertical implantation regions formed by multistage ion implantation in the drift region, the vertical implantation regions having a prescribed vertical implantation width and a prescribed drift region width; an anode electrode disposed on the front surface of the drift region opposite to the semiconductor substrate, the anode electrode being in Schottky contact with the drift region and in ohmic contact with the first conductive type vertical implantation regions; and a cathode electrode disposed on the rear surface of the semiconductor substrate opposite to the drift region, the cathode electrode being in ohmic contact with the semiconductor substrate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device and a method ofmanufacturing the same, and in particular, relates to a semiconductordevice constituted of a Schottky barrier diode (SBD) having a superjunction (SJ) structure, and a method of manufacturing the same.

2. Description of Related Art

Different types of semiconductor devices with the SJ structure have beenproposed. Metal oxide semiconductors (MOS) and field effect transistors(FET) are already disclosed as examples of semiconductor devices havingthe SJ structure (refer to Patent Document 1, for example).

Trench SBDs having SJ structures have also already been disclosed (referto Patent Document 2, for example).

SBDs having the SJ structure have also already been disclosed (refer toPatent Documents 1 to 3, for example).

RELATED ART DOCUMENTS Patent Documents

Patent Document 1: Japanese Patent Application Laid-Open Publication No.2000-40822

Patent Document 2: Japanese Patent Application Laid-Open Publication No.2010-147399

Patent Document 3: Japanese Patent Application Laid-Open Publication No.2008-258313

Patent Document 4: Japanese Patent Application Laid-Open Publication No.2000-349304

Patent Document 5: Japanese Patent Application Laid-Open Publication No.2002-76370

SUMMARY OF THE INVENTION

An object of the present invention is to provide a semiconductor devicewith improved withstand voltage, low leakage current, and low forwardvoltage drop characteristics, and a method of manufacturing the same.

Additional or separate features and advantages of the invention will beset forth in the descriptions that follow and in part will be apparentfrom the description, or may be learned by practice of the invention.The objectives and other advantages of the invention will be realizedand attained by the structure particularly pointed out in the writtendescription and claims thereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, in oneaspect, the present disclosure provides a semiconductor deviceincluding: a first conductive type semiconductor substrate; a firstconductive type drift region formed by epitaxial growth over thesemiconductor substrate; a plurality of second conductive type verticalimplantation regions formed in the drift region by multistage ionimplantation, the second conductive type vertical implantation regionshaving a prescribed vertical implantation width and being at aprescribed distance from each other in the drift region; an anodeelectrode disposed on a front surface of the drift region opposite tothe semiconductor substrate, the anode electrode being in Schottkycontact with the drift region and in ohmic contact with the secondconductive type vertical implantation regions; and a cathode electrodedisposed on a rear surface of the semiconductor substrate opposite tothe drift region, the cathode electrode being in ohmic contact with thesemiconductor substrate.

In another aspect, the present disclosure provides a method ofmanufacturing a semiconductor device including: forming an epitaxialgrowth layer on a substrate; performing multistage ion implantation toform vertical implantation regions in the epitaxial growth layer;performing ion implantation to form field limiting rings in theepitaxial growth layer; performing heat treatment to activate theimplanted ions; forming an insulating layer on an entire surface of theepitaxial growth layer; patterning the insulating layer to form abarrier metal on the epitaxial growth layer; forming an anode electrodeon the barrier metal; and forming a cathode electrode on a rear surfaceof the substrate.

According to the present invention it is possible to provide asemiconductor device with improved withstand voltage, low leakagecurrent, and low forward voltage drop characteristics, and a method ofmanufacturing the same.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory, andare intended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic cross-sectional view of a semiconductor deviceaccording to an embodiment, and FIG. 1B shows a symbol of thesemiconductor device (SBD) of the embodiment.

FIG. 2A is a schematic plan view of a pattern of the semiconductordevice of the embodiment, and FIG. 2B is a schematic cross-sectionalview of FIG. 2A along the line I-I.

FIG. 3A is another schematic plan view of a pattern of the semiconductordevice of the embodiment, and FIG. 3B is a schematic cross-sectionalview of FIG. 3A along the line II-II.

FIG. 4 is a schematic cross-sectional view of an SBD of ComparisonExample 1.

FIG. 5 is a schematic cross-sectional view of an SBD of ComparisonExample 2.

FIG. 6 is a schematic cross-sectional view of an SBD of ComparisonExample 3.

FIG. 7A is a schematic view of an Mnn+ structure of an SBD of acomparison example, and FIG. 7B is a schematic view of an electric fielddistribution in FIG. 7A.

FIG. 8A is a schematic view of the SJ structure of the semiconductordevice of the embodiment, and FIG. 8B is a view of the electric fielddistribution in FIG. 8A.

FIG. 9 is a schematic cross-sectional view of a semiconductor device ofthe embodiment formed by four stage ion implantation.

FIG. 10 is a schematic cross-sectional view of a semiconductor device ofthe embodiment formed by two stage ion implantation.

FIG. 11A is a schematic plan view of a pattern of the semiconductordevice of the embodiment formed by four stage ion implantation, and FIG.11B shows the result of electromagnetic field simulation of thecross-section of FIG. 11A along the line III-III.

FIG. 12 is a schematic cross-sectional view of FIG. 11A along the lineIII-III.

FIG. 13 is a drawing for describing samples (A-1 to A-6) and a referencesample (ref) in which the concentration rate in multistage ionimplantation is changed by a fixed quantity in the semiconductor deviceof the embodiment.

FIG. 14 is a drawing for describing samples (G-1 to G-6) and a referencesample (ref) in which the concentration rate in multistage ionimplantation is changed at a fixed rate in the semiconductor device ofthe embodiment.

FIG. 15 shows dependencies of a withstand voltage BV on refconcentrations (a, b, c) in relation to samples (A-1 to A-6) in whichthe concentration rate is changed by a fixed quantity in the multistageion implantation in the semiconductor device of the embodiment.

FIG. 16 shows dependencies of a withstand voltage BV on refconcentrations (a, b, c) in relation to samples (G-1 to G-6) in whichthe concentration rate is changed at a fixed rate in the multistage ionimplantation in the semiconductor device of the embodiment.

FIG. 17 shows simulation results of electric potential distributions inthe reference samples in the semiconductor device of the embodiment.

FIG. 18 shows simulation results of electric field distributions in thereference samples in the semiconductor device of the embodiment.

FIG. 19 shows dependencies of a withstand voltage BV on epilayerthicknesses (x, y, z) and ref concentrations (a, b, c) in relation tosamples (A-1 to A-6) in which the concentration rate is changed by afixed quantity in the multistage ion implantation in the semiconductordevice of the embodiment.

FIG. 20 shows dependencies of a withstand voltage BV on p verticalimplantation width (α, β) and ref concentrations (a, b, c) in relationto samples (A-1 to A-6) in which the concentration rate is changed by afixed quantity in the multistage ion implantation (ion implantationangle: 7°) in the semiconductor device of the embodiment.

FIG. 21 shows dependencies of a withstand voltage BV on p verticalimplantation width (α, β) and ref concentrations (a, b, c) in relationto samples (A-1 to A-6) in which the concentration rate is changed by afixed quantity in the multistage ion implantation (ion implantationangle: 0°) in the semiconductor device of the embodiment.

FIG. 22 shows dependencies of a withstand voltage BV on p verticalimplantation width (α, β) and ref concentrations (a, b, c) in relationto samples (A-1 to A-6) in which the concentration rate is changed by afixed quantity in the multistage ion implantation (ion implantationangle: 0°, drive temperature: 1050° C.) in the semiconductor device ofthe embodiment.

FIG. 23 shows dependencies of a withstand voltage BV on a p verticalimplantation width (α, β) and ref concentrations (a, b, c) in relationto samples (A-1 to A-6) in which the concentration rate is changed by afixed quantity in the multistage ion implantation (ion implantationangle: 0°, drive temperature: 1100° C.) in the semiconductor device ofthe embodiment.

FIG. 24 shows dependencies of a withstand voltage BV on a p verticalimplantation width (α, β) and ref concentrations (a, b, c) in relationto samples (A-1 to A-6) in which the concentration rate is changed by afixed quantity in the multistage ion implantation (ion implantationangle: 0°, drive temperature: 1150° C.) in the semiconductor device ofthe embodiment.

FIG. 25 shows an example of current/voltage characteristics in a highcurrent region with the drive temperature of the A-2 sample (p verticalimplantation width β; ref concentration b) as a parameter, in thesemiconductor device of the embodiment.

FIG. 26 shows an example of current/voltage characteristics in a lowcurrent region with the drive temperature of the A-2 sample (p verticalimplantation width β; ref concentration b) as a parameter, in thesemiconductor device of the embodiment.

FIG. 27 shows a relation between the withstand voltage BV having the refconcentration (a, b, c) of the A-2 sample (p vertical implantation widthβ; drive temperature: 1050° C.) as a parameter, and the number N_(F) offield limiting rings (FLR), in the semiconductor device of theembodiment.

FIG. 28A shows simulation results for an electric field distributionwhen a voltage just under the withstand voltage (91V) is applied in anA-2 sample (p vertical implantation width=β; 100 KeV; dose=6.0×10¹²atoms/cm²; drive temperature: 1050° C.) with the FLR number N_(F) being2 in the semiconductor device of the embodiment, and FIG. 28B shows anumerical example of an electric field distribution.

FIG. 29A shows simulation results for an electric potential distributionwhen a voltage just under the withstand voltage (91V) is applied in anA-2 sample (p vertical implantation width=β; 100 KeV; dose=6.0×10¹²atoms/cm²; drive temperature: 1050° C.) with the FLR number N_(F) being10 in the semiconductor device of the embodiment, and FIG. 29B shows anumerical example of an electric potential distribution.

FIG. 30A shows simulation results for an electric field distributionwhen a voltage just under the withstand voltage (91V) is applied in anA-2 sample (p vertical implantation width=β; 100 KeV; dose=6.0×10¹²atoms/cm²; drive temperature: 1050° C.) with the FLR number N_(F) being10 in the semiconductor device of the embodiment, and FIG. 30B shows anumerical example of an electric field distribution.

FIG. 31 shows a relation between the withstand voltage BV having the gapL_(F) of the FLRs in the A-2 sample (p vertical implantation=β; drivetemperature: 1050° C.) as a parameter, and the number N_(F) of FLRs, inthe semiconductor device of the embodiment.

FIG. 32 shows a relation between the withstand voltage BV having the Simesa width L₂ in the A-2 sample (p vertical implantation=β; drivetemperature: 1050° C.) as a parameter, and the number N_(F) of FLRs, inthe semiconductor device of the embodiment.

FIG. 33A shows simulation results of an electric field distribution whena voltage just under the withstand voltage is applied (101V) in the A-2sample (p vertical implantation width=β; 100 keV; dose=6.0×10¹²atoms/cm²; FLR number N_(F)=10; drive temperature: 1050° C.) with the Simesa width L₂ and the FLR gap L_(F) being 2.2 μm, in the semiconductordevice of the embodiment, and FIG. 33B shows a numerical example of theelectric field distribution.

FIG. 34A shows simulation results of an electric field distribution whena voltage just under the withstand voltage is applied (101V) in the A-2sample (p vertical implantation width=β; 100 keV; dose=6.0×10¹²atoms/cm²; FLR number N_(F)=10; drive temperature: 1050° C.) with the Simesa width L₂ and the FLR gap L_(F) being 1.6 μm, in the semiconductordevice of the embodiment, and FIG. 34B shows a numerical example of theelectric field distribution.

FIG. 35 is a schematic cross-sectional view in the vicinity of the FLRswhen the FLR number N_(F)=2, in the semiconductor device of theembodiment.

FIG. 36 is a schematic cross-sectional view in the vicinity of the FLRswhen the FLR number N_(F)=10, in the semiconductor device of theembodiment.

FIG. 37 is a schematic cross-sectional view in the vicinity of the FLRswhen the FLR number N_(F)=2, in the semiconductor device of theembodiment formed by four step ion implantation.

FIG. 38 is a schematic cross-sectional view in the vicinity of the FLRswhen the FLR number N_(F)=10, in the semiconductor device of theembodiment formed by four step ion implantation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, an embodiment will be described with reference to drawings. In thedrawings, portions that are the same or similar will be assigned thesame or similar reference characters. However, it should be noted thatthe drawings are schematic, and that the relation between the thicknessand planar dimensions and the ratio of thicknesses of the respectivelayers differ from reality. Thus, specific thicknesses and dimensionsshould be determined based on the description below. Also, there arenaturally portions that differ in dimensional relations and ratios intheir depiction among different drawings.

The embodiment below describes an apparatus and method to specify thetechnical ideas of the present invention, and the embodiment of thepresent invention does not limit the materials, shapes, structures,positions, and the like of the components. The various modifications canbe made to the embodiment of the present invention within the scope ofthe claims.

The schematic cross-sectional structure of a semiconductor device 1 ofan embodiment is as shown in FIG. 1A, and the symbols used for thesemiconductor device 1 of the embodiment are as shown in FIG. 1B.

A schematic plan view of a pattern of the semiconductor device 1 of theembodiment is as shown in FIG. 2A, and a schematic cross-sectional viewof FIG. 2A along the line I-I is as shown in FIG. 2B.

Another schematic plan view of a pattern of the semiconductor device 1of the embodiment is as shown in FIG. 3A, and a schematiccross-sectional view of FIG. 3A along the line II-II is as shown in FIG.3B.

As shown in FIGS. 1 to 3, the semiconductor device 1 of the embodimentincludes: a first conductive-type semiconductor substrate 10; a firstconductive-type drift region 14 formed by epitaxial growth on thesemiconductor substrate 10; a plurality of second conductive-typevertical implantation regions 30 formed in the drift region 14 bymultistage ion implantation, the second conductive-type verticalimplantation regions 30 having a prescribed first vertical implantationwidth L₁ and a prescribed drift region width L₂; an anode electrode 20that is disposed on the front surface of the drift region 14 opposite tothe semiconductor substrate 10, the anode electrode 20 being in Schottkycontact with the drift region 14 and in ohmic contact with the secondconductive-type vertical implantation region 30; and a cathode electrode24 disposed on the rear surface of the semiconductor substrate 10opposite to the drift region 14, the cathode electrode 24 being in ohmiccontact with the semiconductor substrate 10.

As shown in FIG. 1, the anode electrode 20 is in contact with an anodeterminal A, and the cathode electrode 24 is in contact with a cathodeterminal K.

The vertical implantation regions 30 may be formed in the drift region14 in stripes as shown in FIGS. 2A and 2B, or in circular dot patternsas shown in FIGS. 3A and 3B.

As shown in FIGS. 2B and 3B, the vertical implantation regions 30 formedin the drift region 14 have a prescribed vertical implantation width L₁and a prescribed drift region width L₂, and the pitch of the verticalimplantation regions 30 is expressed as L₁+L₂.

As shown in FIG. 1A, the semiconductor device 1 of the embodiment mayinclude a first conductive-type high resistance layer 12 formed byepitaxial growth on the semiconductor substrate 10, and the drift region14 may be disposed on the high resistance layer 12. The firstconductive-type high resistance layer 12 is not necessarily required.The semiconductor device 1 of the embodiment can be given a relativelyhigh withstand voltage by the inclusion of the high resistance layer 12as shown in FIG. 1A.

In the semiconductor device 1 of the embodiment, the multistage ionimplantation includes two or more steps.

In the semiconductor device 1 of the embodiment, the multistage ionimplantation may include four steps, and acceleration energies mayrespectively be 2 MeV, 1.1 MeV, 500 keV, and 100 keV.

In the semiconductor device 1 of the embodiment, the dose when theacceleration energy is 100 keV may be approximately 4×10¹² atoms/cm² toapproximately 8×10¹² atoms/cm², for example. Boron (B) can be used asthe impurity ion, for example.

Also, in the semiconductor device 1 of the embodiment, the dose for whenthe acceleration energy is 500 keV, 1.1 MeV, or 2 MeV may haveconcentration rates at fixed quantities that are approximately 5% to 30%lower than the dose for when the acceleration energy is 100 keV.

Also, in the semiconductor device 1 of the embodiment, the dose for whenthe acceleration energy is 500 keV, 1.1 MeV, or 2 MeV may have fixedconcentration rates that are approximately 5% to 30% lower, for example,than the dose for when the acceleration energy is 100 keV.

In the semiconductor device 1 of the embodiment, the thickness of thedrift region 14 formed by epitaxial growth may be approximately 7 μm toapproximately 9 μm, for example.

In the semiconductor device 1 of the embodiment, the resistivity of thedrift region 14 formed by epitaxial growth may be approximately 0.7 Ωcm,for example.

In the semiconductor device 1 of the embodiment, the drive temperatureand drive time after multistage ion implantation may be respectively1050° C. to 1150° C., and approximately 30 minutes, for example.

In the semiconductor device 1 of the embodiment, the verticalimplantation width L₁ may be approximately 0.8 μm to approximately 1.0μm, for example.

In the semiconductor device 1 of the embodiment, the drift region widthL₂ may be approximately 3.0 μm to approximately 3.2 μm, for example.

Comparison Examples

As shown in FIG. 4, an SBD 1A includes: a first conductive typesemiconductor substrate 100; a first conductive type semiconductor layer120 formed by epitaxial growth on the semiconductor substrate 100; asecond conductive type guard ring diffusion layer 320 formed on thesurface of the semiconductor layer 120; an insulating layer 160 disposedon the front surface of the semiconductor layer 120; a base electrodelayer 180 disposed on the semiconductor layer 120 and insulating layer160 surrounded by the guard ring diffusion layer 320, the base electrodelayer 180 being in Schottky contact with the semiconductor layer 120; ananode electrode 200 disposed on the base electrode layer 180; aninsulating layer 220 disposed on the anode electrode 200; and a cathodeelectrode 240 disposed on the rear surface of the semiconductorsubstrate 100 opposite to the semiconductor layer 120, the cathodeelectrode 240 being in ohmic contact with the semiconductor substrate100.

The base electrode layer 180 is made of Mo, and the anode electrode 200is made of TiAl. The anode electrode 200 is connected to an anodeterminal A, and the cathode electrode 240 is connected to the cathodeterminal K.

As shown in FIG. 5, an SBD 1B of Comparison Example 2 includes: a firstconductive type semiconductor substrate 100; a first conductive typesemiconductor layer 120 formed by epitaxial growth on the semiconductorsubstrate 100; a second conductive type guard ring diffusion layer 320formed on the surface of the semiconductor layer 120; an insulatinglayer 160 disposed on the front surface of the semiconductor layer 120;a base electrode layer 180A disposed on the semiconductor layer 120 andinsulating layer 160 surrounded by the guard ring diffusion layer 320,the base electrode layer 180A being in Schottky contact with thesemiconductor layer 120; an anode electrode 200A disposed on the baseelectrode layer 180A; an insulating layer 220 disposed on the anodeelectrode 200A; and a cathode electrode 240 disposed on the rear surfaceof the semiconductor substrate 100 opposite to the semiconductor layer120, the cathode electrode 240 being in ohmic contact with thesemiconductor substrate 100.

The base electrode layer 180A is made of Mo/Ti in that order from thesemiconductor layer 120, and the anode electrode 200A is made of AlCu.

The SBD 1B according to Comparison Example 2, as shown in FIG. 5 has astep structure on the surface of the semiconductor layer 120, whichincreases the contact area between the base electrode layer 180A and thesemiconductor layer 120, which are in Schottky contact.

As shown in FIG. 6, an SBD 1C according to Comparison Example 3includes: a first conductive type semiconductor substrate 100; a firstconductive type semiconductor layer 120 formed by epitaxial growth onthe semiconductor substrate 100; a second conductive type guard ringdiffusion layer 320 formed on the surface of the semiconductor layer120; an insulating layer 260 formed on an inner wall of a trench formedin the surface of the semiconductor layer 120; a second conductive typepolysilicon region 280 disposed on the insulating layer 260 and thatfills the trench; an anode electrode 200C disposed on the insulatinglayer 260, the polysilicon region 280, and the semiconductor layer 120,the anode electrode 200C being in ohmic contact with the polysiliconregion 280 and in Schottky contact with the semiconductor layer 120; anda cathode electrode 240 disposed on the rear surface of thesemiconductor substrate 100 opposite to the semiconductor layer 120, thecathode electrode 240 being in ohmic contact with the semiconductorsubstrate 100.

The Mnn⁺ structure of the SBDs of the comparison examples areschematically shown in FIG. 7A, and the electric field distribution inthe semiconductor layer 120 of FIG. 7A is schematically shown in FIG.7B. Here, the thickness of the semiconductor layer 120 is d₀. The M(180/180A)/n (semiconductor layer 120)/n⁺ (semiconductor substrate 100)structure corresponds to the SBD portions of FIGS. 4 to 6. As shown inFIG. 7B, in the SBDs of the comparison examples, the electric fielddistribution decreases gradually from anode to cathode.

The SJ structure of the semiconductor device 1 of the embodiment isshown schematically in FIG. 8A, and the electric field distribution inthe drift region 14 of FIG. 8A is schematically shown in FIG. 8B. Here,the thickness of the drift region 14 is d₀. As shown in FIG. 8B, in thesemiconductor device of the embodiment, the electric field distributionis substantially even from anode to cathode.

The areas of the portions with slanted line patterns in FIGS. 7B and 8Bcorrespond to the voltages. Thus, in the semiconductor device of theembodiment, a higher withstand voltage can be attained in the driftregion 14 with the same thickness as the thickness d₀ of thesemiconductor layer 120, compared to the SBDs of the comparisonexamples.

(Multistage Ion Implantation)

The schematic cross-sectional structure of the semiconductor device 1 ofthe embodiment formed by four stage ion implantation is shown in FIG. 9,and the schematic cross-sectional structure of the semiconductor device1 of the embodiment formed by two stage ion implantation is shown inFIG. 10.

As shown in FIG. 9, it is possible to form a p₁ region 30 ₁, a p₂ region30 ₂, a p₃ region 30 ₃, and a p₄ region 30 ₄ corresponding toacceleration energies V₁, V₂, V₃, and V₄ during the four stage ionimplantation. Here, the acceleration energies satisfy the followingrelation: V₁>V₂>V₃>V₄Similarly, in FIG. 10, it is possible to form a p₁region 30 ₁ and a p₂ region 30 ₂ corresponding to acceleration energiesV₁ and V₂. Here, the acceleration energies satisfies a relation ofV₁>V₂. In FIG. 9, DL indicates a region where a depletion layer hasspread from the p vertical implantation region (30 ₁, 30 ₂, 30 ₃, 30 ₄)in the drift region 14. The width of the depletion layer spread regionDL changes depending on the impurity concentration of the p verticalimplantation region (30 ₁, 30 ₂, 30 ₃, 30 ₄) and the n drift region, andthe n drift region width L₂ (Si mesa width). The portion of the n driftregion 14 sandwiched between the p vertical implantation regions (30 ₁,30 ₂, 30 ₃, 30 ₄) may be completely depleted.

The schematic plan view pattern of the semiconductor device 1 of theembodiment formed by four stage ion implantation is shown in FIG. 11A.The result of electromagnetic field simulation in the cross-sectionalong the line III-III of FIG. 11A is as shown in FIG. 11B. In addition,the schematic cross-sectional structure along the line III-III of FIG.11A is shown in FIG. 12.

(Concentration Rate of Multistage Ion Implantation)

In the semiconductor device of the embodiment, the trend of thewithstand voltage BV under the multistage ion implantation condition wasstudied. Here, the thickness of the n drift region 14 (epilayerthickness) was set to 8 μm and the resistivity of the n drift region 14was set to 0.7 Ωcm. The p vertical implantation width L₁ was set to 1.0μm and the n drift region width L₂ (Si mesa width) was set to 3.0 μm.The acceleration energies in the multistage ion implantation (ionimplantation angle: 7°) to form the p vertical implantation regions 30₁, 30 ₂, 30 ₃, and 30 ₄ were set to 2 MeV, 1.1 MeV, 500 keV, and 100keV. The doses at 100 keV were set to 4.0×10¹² atoms/cm², 6.0×10¹²atoms/cm², and 8.0×10¹² atoms/cm². The diffusion drive temperature andtime were respectively set to 1000° C. and 30 minutes.

The description of samples (A-1 to A-6) and a reference sample (ref) inwhich the concentration rate in multistage ion implantation is changedby a fixed quantity in the semiconductor device of the embodiment is asshown in FIG. 13.

The reference sample (ref) has the same concentration rate for the dosein the multistage ion implantation for 100 keV, 500 keV, 1.1 MeV, and 2MeV. That is, the doses are set equal to that of 100 keV.

By contrast, in the A-1 sample, the concentration rates in themultistage ion implantation are changed by a fixed quantity of −5% each,and the concentration rates for the doses at 100 keV, 500 keV, 1.1 MeV,and 2 MeV are respectively 1.00, 0.95, 0.90, and 0.85.

In the A-2 sample, the concentration rates in the multistage ionimplantation are changed by a fixed quantity of −10% each, and theconcentration rates for the doses at 100 keV, 500 keV, 1.1 MeV, and 2MeV are respectively 1.00, 0.90, 0.80, and 0.70.

In the A-3 sample, the concentration rates in the multistage ionimplantation are changed by a fixed quantity of −15% each, and theconcentration rates for the doses at 100 keV, 500 keV, 1.1 MeV, and 2MeV are respectively 1.00, 0.85, 0.70, and 0.55.

In the A-4 sample, the concentration rates in the multistage ionimplantation are changed by a fixed quantity of −20% each, and theconcentration rates for the doses at 100 keV, 500 keV, 1.1 MeV, and 2MeV are respectively 1.00, 0.80, 0.60, and 0.40.

In the A-5 sample, the concentration rates in the multistage ionimplantation are changed by a fixed quantity of −25% each, and theconcentration rates for the doses at 100 keV, 500 keV, 1.1 MeV, and 2MeV are respectively 1.00, 0.75, 0.50, and 0.25.

In the A-6 sample, the concentration rates in the multistage ionimplantation are changed by a fixed quantity of −30% each, and theconcentration rates for the doses at 100 keV, 500 keV, 1.1 MeV, and 2MeV are respectively 1.00, 0.70, 0.40, and 0.10.

The description of samples (G-1 to G-6) and a reference sample (ref) inwhich the concentration rate in multistage ion implantation is changedat a fixed rate in the semiconductor device of the embodiment is asshown in FIG. 14.

The reference sample (ref) has the same concentration rate for the dosein the multistage ion implantation for 100 keV, 500 keV, 1.1 MeV, and 2MeV. That is, the doses are set equal to that of 100 keV.

By contrast, in the G-1 sample, the concentration rates in themultistage ion implantation are changed at a fixed rate of 0.95 timeseach, and the concentration rates for the doses at 100 keV, 500 keV, 1.1MeV, and 2 MeV are respectively 1.00, 0.95, 0.95², and 0.95³.

In the G-2 sample, the concentration rates in the multistage ionimplantation are changed at a fixed rate of 0.90 times each, and theconcentration rates for the doses at 100 keV, 500 keV, 1.1 MeV, and 2MeV are respectively 1.00, 0.90, 0.90², and 0.903.

In the G-3 sample, the concentration rates in the multistage ionimplantation are changed at a fixed rate of 0.85 times each, and theconcentration rates for the doses at 100 keV, 500 keV, 1.1 MeV, and 2MeV are respectively 1.00, 0.85, 0.85², and 0.85³.

In the G-4 sample, the concentration rates in the multistage ionimplantation are changed at a fixed rate of 0.80 times each, and theconcentration rates for the doses at 100 keV, 500 keV, 1.1 MeV, and 2MeV are respectively 1.00, 0.80, 0.80², and 0.80³.

In the G-5 sample, the concentration rates in the multistage ionimplantation are changed at a fixed rate of 0.75 times each, and theconcentration rates for the doses at 100 keV, 500 keV, 1.1 MeV, and 2MeV are respectively 1.00, 0.75, 0.75², and 0.75³.

In the G-6 sample, the concentration rates in the multistage ionimplantation are changed at a fixed rate of 0.70 times each, and theconcentration rates for the doses at 100 keV, 500 keV, 1.1 MeV, and 2MeV are respectively 1.00, 0.70, 0.70², and 0.70³.

In the semiconductor device of the embodiment, the dependencies of thewithstand voltage BV on the ref concentrations a, b, and c with respectto the samples (A-1 to A-6) in which the concentration rate in themultistage ion implantation is changed by a fixed quantity is as shownin FIG. 15, and the dependencies of the withstand voltage BV on the refconcentrations a, b, and c with respect to the samples (G-1 to G6) inwhich the concentration rate in the multistage ion implantation ischanged at a fixed rate is as shown in FIG. 16. The ref concentrationsa, b, and c are impurity concentrations in the p vertical implantationregions 30 corresponding to doses of 4×10¹² atoms/cm², 6×10¹² atoms/cm²,and 8×10¹² atoms/cm² at an acceleration energy of 100 keV, for example.

By the results of FIGS. 15 and 16, a peak withstand voltage BV ofapproximately 120V to 130V is obtained. That is, in the A-3 sample at aref concentration of b, a withstand voltage BV of greater than or equalto approximately 120V is attained, and in the G-4 sample at a refconcentration of b, a withstand voltage BV of greater than or equal to120V is attained.

(Physical Quantity Distribution Just Under Withstand Voltage (100 keV;Dose 6.0×10¹² atoms/cm²))

In the semiconductor device of the embodiment, the simulation results ofthe electric potential distribution of the reference sample (ref) at anapplied voltage of just under the withstand voltage (96V) is as shown inFIG. 17.

The simulation results for the electric field distribution under thesame conditions are as shown in FIG. 18.

(Dependency of Withstand Voltage on Epilayer Thickness/RefConcentration)

The dependency of the withstand voltage BV on the epilayer thickness andthe ref concentration was studied in the semiconductor device of theembodiment. The epilayer thicknesses t_(E) were set to x, y, and z, andthe ref concentrations were set to a, b, and c. The epilayer thicknessesx, y, and z were respectively approximately 7 μm, 8 μm, and 9 μm, withthe resistivity of the n drift region 14 being 0.7 Ωcm, for example. Thep vertical implantation width L₁/n drift region width L₂ (Si mesa width)were set to 1.0 μm/3.0 μm and 0.8 μm/3.2 μm. The acceleration energiesin the multistage ion implantation (ion implantation angle: 7°) to formthe p vertical implantation regions 30 ₁, 30 ₂, 30 ₃, and 30 ₄ were setto 2 MeV, 1.1 MeV, 500 keV, and 100 keV. The doses at 100 keV were setto 4.0×10¹² atoms/cm², 6.0×10¹² atoms/cm², and 8.0×10¹² atoms/cm², forexample. The ref concentrations a, b, and c are impurity concentrationsin the p vertical implantation regions 30 corresponding to doses of4×10¹² atoms/cm², 6×10¹² atoms/cm², and 8×10¹² atoms/cm² at anacceleration energy of 100 keV, for example. The diffusion drivetemperature and time were respectively set to 1000° C. and 30 minutes.

The dependency of the withstand voltage BV on the epilayer thicknesses(x, y, z) and ref concentrations (a, b, c) in relation to samples (A-1to A-6) in which the concentration rate is changed by a fixed quantityin the multistage ion implantation in the semiconductor device of theembodiment is as shown in FIG. 19.

As shown in FIG. 19, when the epilayer thickness is y, the dependency ofthe withstand voltage BV on the ref concentrations a, b, and c is almostunaffected.

(Dependency of Withstand Voltage on p Vertical Implantation Width/Dose)

In the semiconductor device of the embodiment, the dependency of thewithstand voltage BV on the p vertical implantation width L₁ (α, β) andthe ref concentration (a, b, c) in relation to the samples (A-1 to A-6)in which the concentration rate is changed by a fixed quantity in themultistage ion implantation (ion implantation angle: 7°) is as shown inFIG. 20. As for the respective parameters, the epilayer thickness t_(E)is set at a constant 8 μm, the p vertical implantation widths L₁ are αand β, and the ref concentrations are a, b, and c, which correspond tothe respective doses of 4×10¹² atoms/cm², 6×10¹² atoms/cm², and 8×10¹²atoms/cm² at an acceleration energy of 100 keV.

As shown in FIG. 20, in the vicinity of the p vertical implantationwidth β and ref concentration b in the A-2 sample, the withstand voltageBV peaks.

(Dependency of Withstand Voltage on p Vertical Implantation Width/Doseat Ion Implantation Angle of 0°)

The dependency of the withstand voltage BV on the design dimensions wasstudied in the semiconductor device of the embodiment. Here, the ionimplantation angle was changed from 7° to 0°. The thickness of the ndrift region 14 (epilayer thickness) was set to 8 μm with theresistivity of the n drift region 14 being 0.7 Ωcm. The p verticalimplantation width L₁/n drift region width L₂ (Si mesa width) were setto 1.0 μm/3.0 μm and 0.8 μm/3.2 μm. The acceleration energies in themultistage ion implantation (ion implantation angle: 0°) to form the pvertical implantation regions 30 ₁, 30 ₂, 30 ₃, and 30 ₄ were set to 2MeV, 1.1 MeV, 500 keV, and 100 keV. The diffusion drive temperature andtime were respectively set to 1000° C. and 30 minutes.

Dependencies of the withstand voltage BV on the p vertical implantationwidth L₁ (α, β) and ref concentrations (a, b, c) in relation to samples(A-1 to A-6) in which the concentration rate is changed by a fixedquantity in the multistage ion implantation (ion implantation angle: 0°)in the semiconductor device of the embodiment are as shown in FIG. 21.As for the respective parameters, the epilayer thickness t_(E) is set ata constant 8 μm, the p vertical implantation width L₁ is α and β, andthe ref concentrations are a, b, and c, which correspond to therespective doses of 4×10¹² atoms/cm², 6×10¹² atoms/cm², and 8×10¹²atoms/cm² at an acceleration energy of 100 keV, for example.

As shown in FIG. 21, in the vicinity of the p vertical implantationwidth β and ref concentration b in the A-2 sample, the withstand voltageBV peaks, similar to what was shown in FIG. 20.

In the vicinity of the ref concentration a, a higher withstand voltageBV is attained, the reason of which is thought to be the concentrationin the depth direction. When taking into consideration the margin of theprocess, it is preferable that the concentration grade be set such thatthe peak withstand voltage BV decreases but the margin increases. Inother words, it is preferable that the p vertical implantation width βin the A-2 sample be set such that the peak withstand voltage BV isattained in the vicinity of the p vertical implantation width b.

(Withstand Voltage Trend Due to Drive Temperature)

The dependency of the withstand voltage BV on the drive temperature wasstudied in the semiconductor device of the embodiment. Here, the ionimplantation angle was changed from 7° to 0°. The thickness of the ndrift region 14 (epilayer thickness) was set to 8 μm with theresistivity of the n drift region 14 being 0.7 Ωcm. The p verticalimplantation width L₁/n drift region width L₂ (Si mesa width) were setto 1.0 μm/3.0 μm and 0.8 μm/3.2 μm. The acceleration energies in themultistage ion implantation (ion implantation angle: 0°) to form the pvertical implantation regions 30 ₁, 30 ₂, 30 ₃, and 30 ₄ were set to 2MeV, 1.1 MeV, 500 keV, and 100 keV. The diffusion drive temperatureswere set to 1050° C., 1100° C., and 1150° C. and the drive time was setto 30 minutes.

In the semiconductor device of the embodiment, the dependency of thewithstand voltage BV on the p vertical implantation width L₁ (α, β) andref concentration (a, b, c) in relation to the samples (A-1 to A-6) inwhich the concentration rate is changed by a fixed quantity duringmultistage ion implantation (ion implantation angle: 0°; drivetemperature: 1050° C.) is as shown in FIG. 22. As for the respectiveparameters, the epilayer thickness t_(E) is set at a constant 8 μm, thep vertical implantation width L₁ is α and β, and the ref concentrationsare a, b, and c, which correspond to the respective doses of 4×10¹²atoms/cm², 6×10¹² atoms/cm², and 8×10¹² atoms/cm² at an accelerationenergy of 100 keV, for example.

In the semiconductor device of the embodiment, the dependency of thewithstand voltage BV on the p vertical implantation width L₁ (α, β) andref concentration (a, b, c) in relation to the samples (A-1 to A-6) inwhich the concentration rates are changed by a fixed quantity duringmultistage ion implantation (ion implantation angle: 0°; drivetemperature: 1100° C.) is as shown in FIG. 23. As for the respectiveparameters, the epilayer thickness t_(E) is set at a constant 8 μm, thep vertical implantation width L₁ is 1.0 μm and 0.8 μm, and the refconcentrations are a, b, and c, which correspond to the respective dosesof 4×10¹² atoms/cm², 6×10¹² atoms/cm², and 8×10¹² atoms/cm² at anacceleration energy of 100 keV.

In the semiconductor device of the embodiment, the dependency of thewithstand voltage BV on the p vertical implantation width L₁ (α, β) andref concentration (a, b, c) in relation to the samples (A-1 to A-6) inwhich the concentration rates are changed by a fixed quantity duringmultistage ion implantation (ion implantation angle: 0°; drivetemperature: 1150° C.) is as shown in FIG. 24. As for the respectiveparameters, the epilayer thickness t_(E) is set at a constant 8 μm, thep vertical implantation widths L₁ (α, β) are 1.0 μm and 0.8 μm,respectively, and the ref concentrations are a, b, and c, whichcorrespond to the respective doses of 4×10¹² atoms/cm², 6×10¹²atoms/cm², and 8×10¹² atoms/cm² at an acceleration energy of 100 keV,for example.

As shown in FIGS. 22 to 24, as the drive temperature rises, thewithstand voltage BV tends to rise. The peak withstand voltage BV doesnot change greatly. However, because this trend occurs due to theexpansion of diffusion, this also leads to a decreased current path sizein the n drift region 14, and thus, a rise in drive temperature is notnecessarily desirable.

In the vicinity of the p vertical implantation width β and refconcentration b in the A-2 sample, the withstand voltage BV peaks,similar to what was shown in FIGS. 20 and 21.

In the vicinity of the ref concentration a, a higher withstand voltageBV is attained, the reason of which is thought to be the concentrationin the depth direction. When taking into consideration the margin of theprocess, it is preferable that the concentration grade be set such thatthe peak withstand voltage BV decreases but the margin increases. Inother words, it is preferable that the p vertical implantation width L₁in the A-2 sample be set to β such that the peak withstand voltage BV isattained in the vicinity of the p vertical implantation width b.

(Current/Voltage Characteristics)

The dependency of the current/voltage characteristics on the drivetemperature was studied in the semiconductor device of the embodiment.Here, the ion implantation angle was set to 7°. The thickness of the ndrift region 14 (epilayer thickness) was set to 8 μm with theresistivity of the n drift region 14 being 0.7 Ωcm. The p verticalimplantation width L₁/n drift region width L₂ (Si mesa width) were setto 1.0 μm/3.0 μm and 0.8 μm/3.2 μm. The acceleration energies in themultistage ion implantation (ion implantation angle: 7°) to form the pvertical implantation regions 30 ₁, 30 ₂, 30 ₃, and 30 ₄ were set to 2MeV, 1.1 MeV, 500 keV, and 100 keV. Also, the ref concentrations a, b,and c correspond to the respective doses of 4×10¹² atoms/cm², 6×10¹²atoms/cm², and 8×10¹² atoms/cm² at an acceleration energy of 100 keV,for example. The diffusion drive temperatures were set to 1050° C.,1100° C., and 1150° C. and the drive time was set to 30 minutes.

In the semiconductor device of the embodiment, an example ofcurrent/voltage characteristics in a high current region with the drivetemperature of the A-2 sample (p vertical implantation width 0.8 μm;dose 6.0×10¹² atoms/cm²) as a parameter is shown in FIG. 25, and anexample of the current/voltage characteristics in the low current regionis shown in FIG. 26. The drive temperature is changed as follows: 1000°C., 1050° C., 1100° C., and 1150° C.

As shown in FIG. 25, in the high current region, a tendency for theampacity to decrease at a peak of 1050° C. to 1100° C. is observed.Also, as shown in FIG. 26, in the low current region, a pronouncedincrease in drift resistance at a drive temperature of 1150° C. isobserved. Thus, when considering the manufacturing margin, a drivetemperature of approximately 1050° C. is a desirable diffusioncondition.

(FLR Design)

A design of the area outside the semiconductor device of the embodimenthas been studied. Here, the ion implantation angle was set to 7°. Thethickness of the n drift region 14 (epilayer thickness) was set to 8 μmwith the resistivity of the n drift region 14 being 0.7 Ωcm. The pvertical implantation width L₁/n drift region width L₂ (Si mesa width)was set to 0.8 μm/3.2 μm. The acceleration energies in the multistageion implantation (ion implantation angle: 7°) to form the p verticalimplantation regions 30 ₁, 30 ₂, 30 ₃, and 30 ₄ were set to 2 MeV, 1.1MeV, 500 keV, and 100 keV. The diffusion drive temperature was set to1050° C. and the drive time was set to 30 minutes.

In the semiconductor device of the embodiment, the relation between thewithstand voltage BV and the number of FLRs N_(F) with the dose of theA-2 sample (p vertical implantation width=0.8 μm; drive temperature:1050° C.) as a parameter is as shown in FIG. 27.

The ref concentrations a, b, and c correspond to the respective doses of4×10¹² atoms/cm², 6×10¹² atoms/cm², and 8×10¹² atoms/cm² at anacceleration energy of 100 keV, with the respective parameters being asfollows: the epilayer thickness t_(E) is set at 8 μm, the p verticalimplantation width β is 0.8 μm, for example, and the drive temperatureis 1050° C.

As shown in FIG. 27, the same withstand voltage BV can be obtained withthe number of FLRs N_(F) being set at two or greater. However, thewithstand voltage BV is set at 90V to 100V, which is lower than the peakwithstand voltage BV of approximately 120V to 130V attained as shown inFIGS. 15 and 16.

As a result, it can be understood that the FLR needs to be redesigned.The withstand voltage determination point is the distance between thep-type diffusion connected to the anode from the impact ionsusceptibility distribution, and the floating diffusion (FLR, which isnot in contact with electrodes and aims to reduce the electric field)outside of the p-type diffusion. By decreasing the distance, it ispossible to improve the peak withstand voltage BV.

(Physical Quantity Distribution Just Under Withstand Voltage)

In the semiconductor device of the embodiment, the simulation result ofthe electric field distribution when a voltage just under the withstandvoltage is applied (91V) for an A-2 sample (p vertical implantationwidth: 0.8 μm; dose=6×10¹² atoms/cm²; drive temperature: 1050° C.) inwhich the number of FLRs NF is two is as shown in FIG. 28A, and anumerical example of the electric field distribution is as shown in FIG.28B.

In the semiconductor device of the embodiment, the simulation result ofthe electric potential distribution when a voltage just under thewithstand voltage is applied (91V) for an A-2 sample (p verticalimplantation width: 0.8 μm; dose=6×10¹² atoms/cm²; drive temperature:1050° C.) in which the number of FLRs NF is ten is as shown in FIG. 29A,and a numerical example of the electric potential distribution is asshown in FIG. 29B.

The simulation results of the electrical field distribution under thesame conditions is as shown in FIG. 30A, and a numerical example of theelectric field distribution is as shown in FIG. 30B.

(Withstand Voltage and Number of FLRs)

In the semiconductor device of the embodiment, improvement in withstandvoltage by dimensional design of the FLR was studied. Here, the ionimplantation angle was set to 7°. The thickness of the n drift region 14(epilayer thickness) was set to 8 μm with the resistivity of the n driftregion 14 being 0.7 Ωcm. The p vertical implantation width L₁/n driftregion width L₂ (Si mesa width) was set to 0.8 μm/3.2 μm. Theacceleration energies in the multistage ion implantation (ionimplantation angle: 7°) to form the p vertical implantation regions 30₁, 30 ₂, 30 ₃, and 30 ₄ were set to 2 MeV, 1.1 MeV, 500 keV, and 100keV. The doses at 100 keV were set to 4.0×10¹² atoms/cm², 6.0×10¹²atoms/cm², and 8.0×10¹² atoms/cm². The diffusion drive temperature wasset to 1050° C. and the drive time was set to 30 minutes.

In the semiconductor device of the embodiment, the relation between thewithstand voltage BV and the number of FLRs N_(F) with the gap L_(F)between the FLRs in the A-2 sample (p vertical implantation width=0.8μm; drive temperature: 1050° C.) as a parameter is as shown in FIG. 31.

Also, in the semiconductor device of the embodiment, the relationbetween the withstand voltage BV and the number of FLRs N_(F) with theSi mesa width L₂ in the A-2 sample (p vertical implantation width=0.8μm; drive temperature: 1050° C.) as a parameter is as shown in FIG. 32.

In FIGS. 31 and 32, the Si mesa width L₂ is set equal to the FLR gapL_(F).

As shown in FIGS. 31 and 32, when the FLR gap L_(F) (Si mesa width L₂)is 2.3 μm to 2.6 μm the withstand voltage BV tends to be stable.However, a decrease of a few volts from the withstand voltage in a cellof the semiconductor device 1 of the embodiment can be seen. Thisdecrease in voltage results from the usage of a floating FLR.

(Physical Quantity Distribution Just Under Withstand Voltage)

In the semiconductor device of the embodiment, the simulation results ofthe electric field distribution when a voltage just under the withstandvoltage is applied (101V) in the A-2 sample (p vertical implantationwidth=0.8 μm; 100 keV; dose=b atoms/cm²; number of FLRs N_(F)=10; drivetemperature: 1050° C.) with the Si mesa width L₂/FLR gap L_(F)=2.2 μmare as shown in FIG. 33A, and a numerical example of the electric fielddistribution is as shown in FIG. 33B.

In the semiconductor device of the embodiment, the simulation results ofthe electric field distribution when a voltage just under the withstandvoltage is applied (101V) in the A-2 sample (p vertical implantationwidth=0.8 μm; 100 keV; dose=6×10¹² atoms/cm²; number of FLRs N_(F)=10;drive temperature: 1050° C.) with the Si mesa width L₂/FLR gap L_(F)=1.6μm are as shown in FIG. 34A, and a numerical example of the electricfield distribution is as shown in FIG. 34B.

(Schematic Cross-Sectional Structure of Vicinity of FLR)

In the semiconductor device 1 of the embodiment, the schematiccross-sectional structure of the vicinity of the FLR when the number ofFLRs N_(F) is two is as shown in FIG. 35, and the schematiccross-sectional structure of the vicinity of the FLR when the number ofFLRs N_(F) is ten is as shown in FIG. 36.

In the semiconductor device 1 of the embodiment, the n drift regionwidth L₂ (Si mesa width) of the SBD portion may be different from theFLR gap L_(F) in the FLR portion. Alternatively, the n drift regionwidth L₂ (Si mesa width) of the SBD portion may be equal to the gapL_(F) between the FLRs in the FLR portion.

As shown in FIGS. 35 and 36, the semiconductor device 1 of theembodiment includes: the first conductive type semiconductor substrate10; a first conductive type drift region 14 formed by epitaxial growthon the semiconductor substrate 10; the plurality of second conductivetype vertical implantation regions 30 formed in the drift region 14 bymultistage ion implantation, the first conductive vertical implantationregions 30 having the prescribed vertical implantation width L₁ and theprescribed drift region width L₂; the plurality of first conductive typeFLR regions 32 having the prescribed gap L_(F) between the FLRs, thefirst conductive type FLR regions being formed by multistage ionimplantation; the insulating layer 36 disposed on the FLR regions 32,the drift region 14, and the diffusion region 34; the anode electrode 20disposed on the front surface of the drift region 14 opposite to thesemiconductor substrate 10, the anode electrode 20 being in Schottkycontact with the drift region 14 and in ohmic contact with the secondconductive-type vertical implantation regions 30; and the cathodeelectrode 24 disposed on the rear side of the semiconductor substrate 10opposite to the drift region 14, the cathode electrode 24 being in ohmiccontact with the semiconductor substrate 10.

As shown in FIGS. 35 and 36, the anode electrode 20 is connected to theanode terminal A and the cathode electrode 24 is connected to thecathode terminal K.

As shown in FIGS. 2A and 2B, the vertical implantation regions 30 may beformed in a stripe pattern in the drift region 14, and as shown in FIGS.3A and 3B, the vertical implantation regions 30 may be formed in acircular dot pattern.

The FLR regions 32, as shown in FIG. 11A are disposed so as to surroundthe periphery of the SBD portion.

As shown in FIGS. 35 to 36, the vertical implantation regions 30 areformed in the drift region 14 so as to have a prescribed verticalimplantation width L₁ and a prescribed drift region width L₂.

As shown in FIGS. 35 to 36, the FLR regions 32 are formed in the driftregion 14 so as to have prescribed FLR gaps L_(F) therebetween. Thediffusion width of the FLR regions 32 may be set equal to the verticalimplantation width L₁ of the vertical implantation regions 30.

Also, as shown in FIGS. 35 to 36, the semiconductor device 1 of theembodiment may include a first conductive type high resistance layer 12formed by epitaxial growth on the semiconductor substrate 10, with thedrift region 14 being disposed on the high resistance layer 12. Thefirst conductive type high resistance layer 12 is not necessarilyrequired. As shown in FIGS. 35 to 36, the semiconductor device 1 of theembodiment can be made so as to have a relatively high withstand voltageby providing the high resistance layer 12.

In the semiconductor device 1 of the embodiment, the multistage ionimplantation to the FLR regions 32 includes two or more steps.

In the semiconductor device 1 of the embodiment formed by four stage ionimplantation, the schematic cross-sectional view of the vicinity of theFLRs when the number of FLRs N_(F)=2 is as shown in FIG. 37, and thecross-sectional view of the vicinity of the FLRs when the number of FLRsN_(F)=10 is as shown in FIG. 38.

In the semiconductor device 1 of the embodiment, the multistage ionimplantation to the FLR regions 32 ₁, 32 ₂, 32 ₃, and 32 ₄ may includefour steps, and the acceleration energies may be 2 MeV, 1.1 MeV, 500keV, and 100 keV.

Also, in the semiconductor device 1 of the embodiment, the dose when theacceleration energy is 100 keV during multistage ion implantation of theFLR regions 32 ₁, 32 ₂, 32 ₃, and 32 ₄ may be approximately 4×10¹²atoms/cm² to approximately 8×10¹² atoms/cm², for example. Here, theimpurity ion can be boron (B), for example.

In the semiconductor device 1 of the embodiment, in the multistage ionimplantation of the FLR regions 32 ₁, 32 ₂, 32 ₃, and 32 ₄, the dosewhen the acceleration energy is 500 keV, 1.1 MeV, and 2 MeV mayrespectively have a concentration rate of approximately 5% to 30% lessby a fixed quantity compared to the dose for when the accelerationenergy is 100 keV.

In the semiconductor device 1 of the embodiment, in the multistage ionimplantation of the FLR regions 32 ₁, 32 ₂, 32 ₃, and 32 ₄, the dosewhen the acceleration energy is 500 keV, 1.1 MeV, and 2 MeV mayrespectively have a concentration rate of approximately 5% to 30% lessat a fixed rate, for example, compared to the dose for when theacceleration energy is 100 keV.

In the semiconductor device 1 of the embodiment, the diffusion width ofthe FLR regions 32 may be approximately 0.8 μm to approximately 1.0 μm,for example.

In the semiconductor device 1 of the embodiment, the FLR gap L_(F) maybe approximately 1.6 μm to approximately 3.2 μm, for example. It ispreferable that the gap LF be approximately 2.3 μm to 2.6 μm, forexample.

The basic structure of the semiconductor device 1 of the embodiment hasan active SBD region and FLR regions that surround the peripherythereof, and the structure is simple with a small number of layers, witha simple manufacturing method, and thus, the manufacturing cost can bereduced.

Compared to a device with a relatively low-class withstand voltage(approximately 60V or less, for example), the chip size becomes largerdepending on the relative resistance and thickness of the material in adevice with a mid-class withstand voltage (approximately 60V toapproximately 200V, for example), and the main use for mid-classwithstand voltage devices is power systems, and thus, it is possible toimprove performance by reducing series resistance using a highconcentration epitaxial growth layer while achieving high withstandvoltage with an SJ structure.

In other words, in the semiconductor device 1 of the embodiment, theresistivity and thickness of the epitaxial growth layer of the n driftregion 14 are optimized by the SJ structure, thus attaining a mid-classwithstand voltage SBD (approximately 60V to approximately 200V, forexample).

In the semiconductor device 1 of the embodiment, the structure of theFLR regions is optimized and the area of the SBD region in relation tothe chip size is increased, and thus, the area efficiency can beincreased.

In the semiconductor device 1 of the embodiment, in order to improve thewithstand voltage by use of the high concentration epitaxial growthmaterial, the FLR regions can be made by the trench field platetechnique. In other words, as shown in FIGS. 36 to 38, a structure inwhich the electric field is reduced is formed by forming the FLR regions32 (32 ₁, 32 ₂, 32 ₃, and 32 ₄) by the SJ structure, and extending ananode electrode 20 over the FLR regions 32 (32 ₁, 32 ₂, 32 ₃, and 32 ₄)across the insulating layer 36.

In the semiconductor device 1 of the embodiment, the use of the SJstructure in the SBD region allows for the junction FET effect in the pvertical implantation regions 30, and thus, it is possible to mitigatereverse leakage current in the SBD.

As a result, in the embodiment, an SBD with an improved performance andlow cost SJ structure at a mid-class withstand voltage is attained.

In the semiconductor device 1 of the embodiment, in order to improvewithstand voltage while using the high concentration epitaxial growthmaterial, the SJ structure including the p vertical implantation regions30 (30 ₁, 30 ₂, 30 ₃, 30 ₄) formed by multistage ion implantation andthe n drift region 14 is used.

In the semiconductor device 1 of the embodiment, it is possible tomitigate leakage current by using the SJ structure while simultaneouslyattaining a low forward voltage V_(F). Thus, in the semiconductor device1 of the embodiment, it is possible to attain a mid-class withstandvoltage, a low forward voltage VF, and low leakage current.

Furthermore, in the semiconductor device 1 of the embodiment, it ispossible to attain low ON voltage by the conductive modulation effect bythe junction of the p vertical implantation region (30), the n driftregion (14), and the n⁺ substrate (10) in the high current region, dueto forward voltage characteristics.

In the semiconductor device 1 of the embodiment, the following processconditions and dimensions are used as attainable conditions formid-class withstand voltage devices (60V to 100V).

The thickness of the n drift region 14 (thickness of epitaxial growthlayer) was set at 7 μm, 8 μm, and 9 μm, with the resistivity of the ndrift region 14 being 0.7 Ωcm. The p vertical implantation width L₁/ndrift region width L₂ (Si mesa width) were set to 1.0 μm/3.0 μm and 0.8μm/3.2 μm. The acceleration energies in the multistage ion implantation(ion implantation angle: 7°) to form the p vertical implantation regions30 ₁, 30 ₂, 30 ₃, and 30 ₄ were set to 2 MeV, 1.1 MeV, 500 keV, and 100keV. The doses at 100 keV were set to 4.0×10¹² atoms/cm², 6.0×10¹²atoms/cm², and 8.0×10¹² atoms/cm². The diffusion drive temperature andtime were respectively set to 1000° C./1050° C./1100° C./1150° C. and 30minutes.

(Manufacturing Method)

A method of manufacturing the semiconductor device of the embodimentincludes: a step of preparing the substrate 10; a step of forming anepitaxial growth layer (n drift region 14) on the substrate 10; a stepof forming an insulating film on the epitaxial growth layer (n driftregion 14); a step of patterning the insulating film and performingmultistage ion implantation to form the SJ structure of the SBD portion;a step of patterning the insulating film and performing ion implantationto form the FLRs in the FLR portion; a step of performing a driveprocess to diffuse the impurities implanted by multistage ionimplantation to form the SJ structure in the SBD portion and ionimplantation to form the FLRs of the FLR portion; a step of forming theinsulating layer 36 (refer to FIGS. 35 to 38) over the entire devicesurface; a step of patterning the insulating layer 36 and forming abarrier metal to form a Schottky contact with the n drift region 14 ofthe SBD portion; a step of forming the anode electrode 20 on the barriermetal; a step of forming a protective film on the entire surface of thedevice; and a step of forming the cathode electrode 24 on the rearsurface of the substrate 10.

In the steps above, the insulating layer 36 is a multilayer filmincluding an SiO₂ film and a PSG film, with respective thicknesses ofapproximately 6,000 Å and 15,000 Å, for example.

Also, the etching process performed to form the Schottky contact withthe n drift region 14 of the SBD portion is preferably wet etching.

The barrier metal to form the Schottky contact with the n drift region14 of the SBD portion can be Ti/TiN, Mo, or the like, for example.

The anode electrode 20 formed on the barrier metal can be an AlCu alloywith a thickness of approximately 4.2 μm, for example.

An SiN film approximately 8,000 Å in thickness, for example, can be usedas the protective film to cover the entire surface of the device.

The cathode electrode 24 can be made of a TiNiAuAg alloy, for example.

As described above, according to the present embodiment, it is possibleto provide a Schottky barrier diode with improved withstand voltage, lowleakage current, and low forward voltage drop.

OTHER EMBODIMENTS

An embodiment was disclosed above, but the description and drawingsconstituting a portion of the disclosure are merely examples, and do notlimit the invention. Various substitute embodiments, examples, andapplied techniques should be clear to a person skilled in the art basedon this disclosure.

For example, in the semiconductor device of the embodiment, a siliconsubstrate was described as an example, but an SiC or GaN-typesemiconductor material may be used as another type of semiconductormaterial, for example.

In this manner, the present invention includes various embodiments andthe like not disclosed here.

INDUSTRIAL APPLICABILITY

The semiconductor device of the present invention can be widely used inpower devices such as Si power semiconductor modules, SiC powersemiconductor modules, and intelligent power modules, and in particular,can be used in inverters and converters for vehicles, solar cells, andindustrial equipment where miniaturization, and low weight are desired.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover modifications and variationsthat come within the scope of the appended claims and their equivalents.In particular, it is explicitly contemplated that any part or whole ofany two or more of the embodiments and their modifications describedabove can be combined and regarded within the scope of the presentinvention.

What is claimed is:
 1. A semiconductor device, comprising: a firstconductive type semiconductor substrate; a first conductive type driftregion formed by epitaxial growth over the semiconductor substrate; aplurality of second conductive type vertical implantation regions formedin the drift region by multistage ion implantation, the secondconductive type vertical implantation regions having a prescribed widthand being at a prescribed distance from each other in the drift region;an anode electrode disposed on a front surface of the drift regionopposite to the semiconductor substrate, the anode electrode being inSchottky contact with the drift region and in ohmic contact with thesecond conductive type vertical implantation regions; and a cathodeelectrode disposed on a rear surface of the semiconductor substrateopposite to the drift region, the cathode electrode being in ohmiccontact with the semiconductor substrate.
 2. The semiconductor deviceaccording to claim 1, wherein a thickness of the drift region formed bythe epitaxial growth is 7 μm to 9 μm.
 3. The semiconductor deviceaccording to claim 1, wherein a resistivity of the drift region formedby the epitaxial growth is 0.7 Ωcm.
 4. The semiconductor deviceaccording to claim 1, wherein said width of the vertical implantationregions is 0.8 μm to 1.0 μm.
 5. The semiconductor device according toclaim 1, wherein said distance between the vertical implantation regionsis 3.0 μm to 3.2 μm.
 6. The semiconductor device according to claim 1,wherein the drift region includes a prescribed number of field limitingrings formed around an area where the vertical implantation regions areformed.
 7. The semiconductor device according to claim 6, wherein thenumber of said field limiting rings is two or greater.
 8. Thesemiconductor device according to claim 7, wherein a gap between thefield limiting rings is 1.6 μm to 3.2 μm.
 9. The semiconductor deviceaccording to claim 8, wherein the gap between the field limiting ringsis 2.3 μm to 2.6 μm.
 10. The semiconductor device according to claim 1,wherein the vertical implantation regions are formed in the drift regionso as to form a stripe pattern or dot pattern in a plan view.
 11. Thesemiconductor device according to claim 1, further comprising a firstconductive type high resistance layer formed by epitaxial growth on thesemiconductor substrate, wherein the drift region is formed on the highresistance layer.
 12. The semiconductor device according to claim 6,further comprising an insulating layer disposed on the field limitingrings, wherein the anode electrode extends over the field limiting ringsacross the insulating layer.
 13. A method of manufacturing asemiconductor device, comprising: forming an epitaxial growth layer on asubstrate; performing multistage ion implantation to form verticalimplantation regions in the epitaxial growth layer; performing ionimplantation to form field limiting rings in the epitaxial growth layer;performing heat treatment to activate the implanted ions; forming aninsulating layer on an entire surface of the epitaxial growth layer;patterning the insulating layer to form a barrier metal on the epitaxialgrowth layer; forming an anode electrode on the barrier metal; andforming a cathode electrode on a rear surface of the substrate.
 14. Themethod of manufacturing a semiconductor device according to claim 13,wherein the multistage ion implantation includes two or more steps. 15.The method of manufacturing a semiconductor device according to claim13, wherein the multistage ion implantation includes four steps, withacceleration energies respectively being 2 MeV, 1.1 MeV, 500 keV, and100 keV.
 16. The method of manufacturing a semiconductor deviceaccording to claim 15, wherein a dose when an acceleration energy is 100keV is 4×10¹² atoms/cm² to 8×10¹² atoms/cm².
 17. The method ofmanufacturing a semiconductor device according to claim 16, wherein aconcentration rate of the dose at the acceleration energy of 500 keV isreduced by a fixed quantity of 5% to 30% of the dose at the accelerationenergy of 100 keV, a concentration rate of the dose at the accelerationenergy of 1.1 MeV is reduced by said fixed quantity from the dose at 500keV, and a concentration rate of the dose at the acceleration energy of2 MeV is reduced by said fixed quantity from the dose at 1.1 MeV. 18.The method of manufacturing a semiconductor device according to claim16, wherein a concentration rate of the dose at an acceleration energyof 500 keV is reduced from the dose at the acceleration energy of 100keV at a fixed rate of 5% to 30%, a concentration rate of the dose atthe acceleration energy of 1.1 MeV is reduced from the dose at 500 keVat said fixed rate, and a concentration rate of the dose at theacceleration energy of 2 MeV is reduced from the dose at 1.1 MeV at saidfixed rate.
 19. The method of manufacturing a semiconductor deviceaccording to claim 13, wherein, after the multistage ion implantation,heat treatment is performed at a temperature of 1050° C. to 1150° C. anda time of 30 minutes.
 20. The method of manufacturing a semiconductordevice according to claim 13, wherein the step of performing multistageion implantation and the step of performing ion implantation areperformed at the same time.